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BTS guideline
22.
tration should be adjusted upwards or downwards to maintain the target saturation range. [Grade D] In most emergency situations oxygen is given to patients immediately without a formal prescription or drug order. The lack of a prescription should never preclude oxygen being given when needed in an emergency situation. However, a subsequent written record must be made of what oxygen therapy has been given to every patient (in a similar manner to the recording of all other emergency treatment). [Grade D]
Patients with COPD may also use terms such as chronic bronchitis and emphysema to describe their condition but may sometimes mistakenly use ‘‘asthma’’ (see table 3).
9.6 Other patients at risk of hypercapnic respiratory failure with respiratory acidosis c
c
c
9.4 Patients with known COPD A proportion of breathless patients will have COPD (chronic bronchitis and emphysema). Unfortunately, a recent Cochrane review of oxygen therapy for COPD in the prehospital setting found no relevant studies.282 Audits of emergency admissions in UK hospitals have shown that about 25% of breathless medical patients who require hospital admission have COPD as a main diagnosis. Many of these patients will require carefully controlled oxygen therapy because they are at risk of carbon dioxide retention or respiratory acidosis. In a large UK study,34 47% of patients with exacerbated COPD had PaCO2 .6.0 kPa (45 mm Hg), 20% had respiratory acidosis (pH ,7.35 or [H+] .45 nmol/l) and 4.6% had severe acidosis (pH ,7.25 or [H+] .56 nmol/l). Acidosis was more common if the blood oxygen was .10 kPa (75 mm Hg). Plant and colleagues34 recommended that patients with acute COPD should be maintained within a PaO2 range of 7.3–10 kPa (55–75 mm Hg) to avoid the dangers of hypoxaemia and acidosis.
Recommendation (see table 3) c
Patients with COPD should initially be given oxygen via a Venturi 28% mask at a flow rate of 4 l/min or a 24% Venturi mask at a flow rate of 2 l/min. Some patients may benefit from higher flow rates via the Venturi mask (see recommendation 32). The target oxygen saturation should be 88– 92% in most cases or an individualised saturation range based on the patient’s blood gas measurements during previous exacerbations. [Grade C]
9.5 Patients who should be assumed to have COPD One of the challenges faced by the initial clinical response staff is that the diagnosis may be unclear and the patient’s medical records or detailed history may not be available. It has been shown that ambulance teams may be aware of a diagnosis of COPD in only 58% of cases.283 The guidelines group consider that an initial diagnosis of COPD should be assumed if there is no clear history of asthma and the patient is .50 years of age and a long-term smoker or ex-smoker with a history of longstanding breathlessness on minor exertion. The diagnosis should be reassessed on arrival at hospital where more information will probably become available, and the FEV1 should be measured unless the patient is too breathless to undertake spirometry.
Recommendation c
vi46
If the diagnosis is unknown, patients .50 years of age who are long-term smokers with a history of chronic breathlessness on minor exertion such as walking on level ground and no other known cause of breathlessness should be treated as if having COPD for the purposes of this guideline.
c
c c c
Any patient with severe kyphoscoliosis or severe ankylosing spondylitis. Severe lung scarring from old tuberculosis (especially with thoracoplasty). Morbid obesity (body mass index .40 kg/m2). Patients with neuromuscular disorders (especially if muscle weakness has led to wheelchair use). Any patient on home mechanical ventilation. Use of home mechanical ventilation. Overdose of opiates, benzodiazepines or other drugs causing respiratory depression.
9.7 Oxygen alert cards and 24% or 28% Venturi masks in patients with COPD (and others at risk of respiratory acidosis) who have had an episode of hypercapnic respiratory failure The administration of high oxygen concentrations in acute COPD and other conditions (see section 8.12) leads to worsening of hypercapnic respiratory failure and respiratory acidosis.34 Patients with COPD and a PaO2 .10 kPa (75 mm Hg) and a PaCO2 .6.0 kPa (45 mm Hg) may be assumed to have had excessive oxygen therapy. If a patient is found to have respiratory acidosis due to excessive oxygen therapy, the oxygen therapy should not be discontinued immediately because the oxygen level will fall significantly over 1–2 min by virtue of the alveolar gas equation (see section 5.2.1) whereas the carbon dioxide level will take much longer to correct itself (see section 6.3.2). In this situation the oxygen treatment should be stepped down to 28% or 24% oxygen from a Venturi mask depending on oxygen saturation and blood gas results. A saturation target of 88–92% is recommended for acidotic patients in type 2 respiratory failure and non-invasive ventilation is required if the acidosis does not resolve quickly.25 34 This avoidable problem has occurred historically during the transfer to hospital, prior to measurement of arterial blood gases or before a definitive diagnosis is known. Furthermore, ambulance teams are often not informed at present of a diagnosis of COPD283 and may not be aware of the presence of other high-risk conditions such as kyphoscoliosis or respiratory failure due to neuromuscular conditions. These patients can be issued with an oxygen alert card and a 24% or 28%Venturi mask based on previous blood gas results. The recommended oxygen saturation will be based on the clinical scenario for each individual patient but will usually be 88–92%, occasionally 85–88% or 85–90% based on previous blood gas results. Patients should be instructed to show this card to the ambulance crew and emergency department staff in order to avoid the use of high oxygen concentrations. This scheme can be successful.284 The ambulance service can also be informed about which patients are issued with oxygen alert cards.285 The current Joint Royal Colleges Ambulance Liaison Committee (JRCALC) guideline for the use of oxygen in COPD are being revised to accommodate these changes.274 An example of an oxygen alert card is shown in fig 8.
Recommendations 23.
Patients with COPD (and other at-risk conditions) who have had an episode of hypercapnic respiratory failure should be issued with an oxygen alert card Thorax 2008;63(Suppl VI):vi1–vi68. doi:10.1136/thx.2008.102947